Lattice dynamics of LiH, LiF and LiCl

Abstract

The electron charge density maps as determined by X-ray diffraction experiments lead to the conclusion that the charge transfer in lithium fluoride is about 0.88e rather than 1.0e usually accepted for all the alkali halides. A theoretical investigation of the lattice vibrations in LiH, LiF and LiCl has been carried out with a view to obtaining an independent check on this observation of partial charge transfer. The model used is a modified shell model which takes account of three body overlap forces arising in ionic solids due to nonorthogonality of free-ion wavefunctions and in which the valence Z of an ion enters as an independent parameter. It would appear that Z=0.88 is a more appropriate choice than Z=1.0.